The W3C Web Services Activity has published a note on Semantic Annotations for WSDL and XML Schema — Usage Guide. "Web services provide a standards-based foundation for exchanging information between distributed software systems. The W3C Recommendation Web Services Description Language (WSDL) specifies a standard way to describe the interfaces of a Web Service at a syntactic level and how to invoke it. While the syntactic descriptions provide information about the structure of input and output messages of an interface and about how to invoke the service, semantics are needed to describe what a Web service actual does. These semantics, when expressed in formal languages, disambiguate the description of Web services interfaces, paving the way for automatic discovery, composition and integration of software components. WSDL does not explicitly provide mechanisms to specify the semantics of a Web service. Semantic Annotations for WSDL and XML Schema (SAWSDL) defines mechanisms by which semantic annotations can be added to WSDL components. This usage guide is an accompanying document to SAWSDL specification. It presents examples illustrating how to associate semantic annotations with a Web service. These annotations could be used for classifying, discovering, matching, composing, and invoking Web services."
